Finely dice the garlic and sauté with the leek in the excess fat from the bacon over medium heat. A few minutes later add the tomatoes and season with pepper.
Melt the butter in another saucepan, add the flour and sweat while stirring constantly. Add some milk and keep stirring. Simmer over a low flame and repeat the process until the milk is empty. Season with nutmeg, pepper and salt. The result should be a creamy, thick sauce. If necessary, add flour and bring to the boil again while stirring.
Cover the tortillas with the leek vegetables, the bacon strips and 2 tablespoons of sauce and roll up. Pour into a small, greased casserole dish and pour the rest of the sauce over it. Finally, top with the cheese and place in the preheated oven at 175 ° C for about 30 minutes.